This portion of the discussion is surprisingly problematic. I will deal with the range F4 to F5 inclusive. This is called the middle register because it lies in the middle of the total female range. The fully-functional female range has a modal span beginning at F3 (a fifth below middle C)and ending at F6 (the Queen of the Night’s famous high F). This is controversial nowadays because not many singers access those notes. That is because the flute voice is left undeveloped and therefore a correct muscular balance in the extreme high range becomes difficult. I will deal with the female high range in a future post, but suffices it to say that the upper end is rarely fully explored.
As for the middle range, as always, we must consider both the muscular and acoustic problems.
1. Muscular: We have already established that the “real voice” (the modal dynamic that involves muscular antagonism between vocalis and CT) spans about 3 octaves. This means that halfway through that range should be the muscular shift. I have been of the mind set that the muscular shift was around F5, but this does not compute. The second passaggio (between E5-G5) is an acoustic shift where the first formant takes over the resonance again. The muscular shift probably happens around C5. A colleague of mine in my early days of teaching in Utah mentioned this once and I did not comment on it. It seemed logical then, but I did not have the information to back it up. But when we think of it, it is around C5 or there about that female voices reach a lighter mechanism. If a woman takes what she calls the chest voice up, the voice usually will crack around Bb4-C5 where the muscular shift should occur. That is why Agnes Baltsa exhibited a muscular shift around C5 in the Carmen clip featured in the previous post.
The acoustic problem with the female middle voice is that the adjustments necessary for the ideal second formant tuning is not so easily achieved. In fact most female singers go in and out of second formant tuning in the middle range. Because of this difficulty many singers attempt to get closer to the first formant tuning (belt tuning) or more commonly some non-resonant tuning between the two. This is why the female middle voice is so often not resonant. The best that can be found among our most accomplished operatic divas is a high percentage of second formant tuning in the middle range. Even the best singers tend to revert to 1st formant or non-resonant adjustments.
In short the best middle voice models are rarities both in terms of muscular adjustments and in terms of acoustic adjustments. When I was preparing this post, I expected to find many singers on Youtube.com that I could acoustically analyze to prove my point. I was disappointed. The next question then could be that my expectations are wrong. I thought of this. But acoustic theory is based on pitch level and its interaction with the vocal tract (vowels). It is a relatively simple thing to observe relative to the limits of vowel formants. Formant dominance in the male voice tends to be easier to distinguish. Male singers either correctly tune to F2 above their respective passaggio or else remain F1-dominant. They do not tend to go back and forth. The reason for this can only be one thing, namely that male voices sing in a range conducive to vocalic intelligibility. Even the F2 range for male voices requires only mild modification. Male singers also accept that high notes necessitate modification and that the viability of the resonance adjustment for high notes trumps vocalic purity. Women will conform to this in their high range but find it more difficult to accept that substantial modification of vowels is necessary in their middle range. Many women do not believe that such extremely modified vowels will sound intelligible in context. So they sabotage their own resonance viability for a feeling of vocalic satisfaction. Paradoxically, that feeling of vocalic satisfaction is precisely what hinders viable resonance and therefore any real chance at intelligibility in context.